The present invention relates to an automatic paper feeder, more particularly to an automatic paper feeder in which a conveyance roller is provided between a paper feed roller and the platen of a printer.
A sheet of paper, which is shorter at the edge thereof in the direction of feeding of the sheet of paper than at the other edge thereof across the direction as a slip and a horizontally slender postcard, is generally required to be 10 accurately fed from an automatic paper feeder to the platen of a printer. For that reason, an automatic paper feeder having a second conveyance roller between a paper feed roller as a first conveyance roller at a paper supply bin and the platen of a printer, has been developed as disclosed in the Japan Utility Model Application (OPI) No. 83561/89 (the term "OPI" as used herein means an "unexamined published application"). The latter automatic paper feeder is described with reference to FIGS. 16 through 24 from now on. The feeder 1 is removably attached to the printer 2. The feeder 1 includes the paper supply bin 3 in which sheets of blank paper are stacked together in a titled posture, and a paper reception bin 4 in which the sheets of printed paper are stacked together. A first paper feed roller shaft 6 is rotatably supported by the right and left side plates 5A and 5B of the body frame 5 of the feeder 1, and horizontally extends between the side plates. The body of a first paper feed roller 7, which is put in pressure contact with the outermost sheet of blank paper, is mounted on the intermediate portion of the first paper feed roller shaft 6. A clutch 8 is attached to the shaft 6 at the end thereof to transmit torque to the shaft at appropriate timing. A second paper feed roller shaft 9, which is a conveyance roller shaft, is rotatably supported by the side plates 5A and 5B, and horizontally extends between them in parallel with the first paper feed roller shaft 6. The body of a second paper feed roller 10, which is a conveyance roller, is mounted on the intermediate portion of the second paper feed roller shaft 9, located nearly in the middle of the distance between the first paper feed roller 7 and the platen 16 of the printer 2, and smaller in outside diameter than that of the first paper feed roller 7. The body of a roller 12 is mounted on a shaft 11 rotatably supported by the side plates 5A and 5B and extending between them, and is located in pressure contact with that of the second paper feed roller 10. A paper discharge roller shaft 13 is rotatably supported by the side plates 5A and 5B, and horizontally extends between them. The body of a paper discharge roller 14 is mounted on the intermediate portion of the paper discharge roller shaft 13. A roller 15 is provided in presser contact with the paper discharge roller 14.
The platen 16 of the printer 2 is secured to a rotary shaft 17 rotatably supported by the body of the printer and extending horizontally. A platen gear 18 is provided on the rotary shaft 17. Torque is transmitted from a motor 19 to the platen gear 18 through a drive gear 19A and an idle gear 20. The first paper feed roller 7 is kinematically coupled to the rotary shaft 17 through a torque transmission gear train 21 provided at the side plate 5B, and the clutch 8. The gear 22A of a bushing gear unit 22 for transmitting torque to the second o paper feed roller shaft 9 is engaged with an idle gear 21A of the gear train 21.
As shown in FIGS. 18 and 19, the bushing gear unit 22 includes the gear 22A and a cylindrical portion 22B integrated with the gear concentrically thereto and rotatably fitted in the side plate 5B of the body frame 5. The cylindrical portion 22B has an engagement notch 23 at the end of the portion. A one-way bearing 24 is provided in the cylindrical portion 22B, and includes an inner race 24A and an outer race 24B formed with a jut 24C on the peripheral surface of the outer race.
The second paper feed roller shaft 9 is pivotally fitted at one end thereof in the inner race 24A of the one-way bearing 24. The bearing 24 transmits forward turning power to the second paper feed roller shaft 9 only when the bushing gear unit 22 is rotated forward. In other words, the bearing 24 does not transmit backward turning power to the shaft 9 when the gear unit 22 is rotated backward or the outer race 24B of the bearing is rotated backward.
When a paper feed instruction is sent out from the control section of the printer 2, the motor 19 is put in action to transmit torque to the rotary shaft 17 through the drive gear 19A and the idle gear 20 to rotate the platen 16. The torque of the rotary shaft 17 is transmitted to the gear train 1 and the clutch 8 so that the cylindrical portion 22B of the bushing gear unit 22 is rotated through the idle gear 21A of the gear train and the gear 22A engaged with the idle gear. The torque of the bushing gear unit 22 being rotated synchronously with the platen 16 is transmitted to the second paper feed roller shaft 9 so that the outer race 24B of the one-way bearing 24 is rotated synchronously with the forward rotation of the bushing gear unit. Torque is not transmitted to the inner race 24A of the one-way bearing 24 when the bushing gear unit 22 is rotated backward.
If the printer 2 is a dot printer, a line printer or the like and is capable of printing characters of normal height, characters of double height, a vertical line, an exponent and so forth and the character of double height, the vertical line or the like is to be printed by the printer, the sheet of paper is first fed by a length for two horizontal lines through the use of the automatic paper feeder 1, the lower portion of the character, the vertical line or the like is then printed on the sheet of paper, the sheet of paper is thereafter moved back by a length for one horizontal line, and the upper portion of the character, the line or the like is then printed on the sheet of paper. When the sheet of paper is moved back by the length for one horizontal line after being fed by the length for two horizontal lines, the sheet of paper is loosened between the second paper feed roller 10 and the platen 16 due to the operation of the one-way bearing 24 provided concentrically to the roller. The reason for the loosening is that since the jut 24C of the one-way bearing 24 is engaged in the engagement notch 23 of the bushing gear unit 22, the second paper feed roller 10 remains stopped throughout the backward rotation of the platen 16 to result in loosening the sheet of paper and the sheet of paper is thereafter fed by the same length at the roller and the platen through the forward rotation of the platen while remaining loosened. When such printing is repeated, the loosening of the sheet of paper is cumulated to cause it to undergo bending, improper feeding or the like.
The cause of the loosening of the sheet of paper is described in detail from now on, with reference to sequential steps shown in FIGS. 20, 21, 22, 23 and 24. The upper and lower portions of each of these drawings show the positional relationship between the one-way bearing 24 and the bushing gear unit 22 and the operational relationship between the second paper feed roller 10 and the platen 16, respectively. When the platen 16 is rotated forward to feed the sheet of paper by a length for two horizontal lines in order to print a character of double height on the paper by the printer 2, after the printing of a character of normal height in a first row on the paper, for example, the bushing gear unit 22 is rotated forward synchronously with the platen so that the jut 24C of the one-way bearing 24, which is engaged in the engagement notch 23 of the bushing gear unit, is turned forward to rotate the second paper feed roller 10, as shown in FIG. 20. The lower half of the character of double height is then printed in a second row on the sheet of paper. After that, the platen 16 is rotated backward by a length for one horizontal line in order to print the upper half of the character of double height on the sheet of paper, as shown in FIG. 21. At that time, the jut 24C of the one-way bearing 24 is turned backward, torque is not transmitted through the inner and outer races 24A and 24B of the bearing, the inner race is not rotated backward synchronously with the platen 16, and the second paper feed roller shaft 9 remains stopped, so that the paper is loosened. In this step, the upper half of the character of double height is printed in the second row on the sheet of paper. When a character of double height is to be then printed in a third row on the sheet of paper by the printer 2 in the steps shown in FIGS. 22 and 23, the platen 165 is rotated forward to feed the sheet of paper by a length for three horizontal lines. For that purpose, the platen 16 is first rotated forward to rotate the second paper feed roller shaft 9 through the one-way bearing 24 to feed the sheet of paper by a length for one horizontal line to move out the lower half of the second-row character of double height from under the printing head of the printer 2 in the step shown in FIG. 22. At that time, since the sheet of paper is fed by both the platen 16 and the second paper feed roller 10, the paper remains loosened. The platen 16 is thereafter rotated forward to feed the sheet of paper by a length for two horizontal lines to print the lower half of the character of double height in the third row on the sheet of paper in the step showing FIG. 23. The platen 16 is then rotated backward to move back the sheet of paper by a length for one horizontal line to print the upper half of the character of double height in the third row on the sheet of paper in the step shown in FIG. 24, thus completing the printing of the character of double height in the third row on the sheet of paper. At that time, because of the operation of the one-way bearing 24, the second paper feed roller shaft 9 is not rotated backward but remains stopped. For that reason, the sheet of paper undergoes loosening by a length for one horizontal line in addition to the former loosening by a length for one horizontal line, so that the sheet of paper is resultantly loosened by a length for two horizontal lines. In other words, the sheet of paper is cumulatively loosened the same number of times as the moving-back thereof. This is a problem.